1. Field of the Invention
The present invention is directed to an improved sanitary valve design. In particular, the present invention is directed to a sanitary valve design that allows for free-drainage of process and sterilizing and cleaning materials.
2. Description of Background Art
There have been many incidents where sanitary processes have failed, resulting in loss of product. In some cases, harm to consumers occurs. In many instances the specific nature of the source of contamination remains unidentified. In many other instances; however, the source of contamination has been traced back to drain valves, which have not been properly cleaned, and in many cases where procedures specify it, sterilized between production runs.
Failures have not been limited to valve designs traditionally viewed as being problematic when used in sanitary applications (tulip and kettle valves, plug and ball valves, e.g.) but, rather, extend to include weir and radial diaphragm valve designs which are currently considered state-of-the-art designs particularly suited for sanitary processing applications.
The causes for these failures, almost without exception, relate to material accumulation in low, undrainable pooling areas and in tight crevice areas, particularly those associated with moving parts such as sliding or rotating O-ring seals. Deep, tight joints, particularly around moving parts, are primary sites for material to accumulate and are ideal safe havens for microbial proliferation. These sites can become tightly packed with highly nutricious process materials, which provide insulation and protection from cleaning and sterilizing agents, allowing significant microbial populations to develop over time. Deposits of tightly adhering organic and inorganic material resist the effects of caustic and acidic cleaning solutions, mechanical shear from agitation and high rates of circulation and from the effects of steam sterilization. Large deposits may develop in valves over time, a consequence of the selection of valves emphasizing design robustness and mechanical reliability over in-situ process cleanability and sterilizability. Cleaning and sterilizing followed by the initiation of process production may cause large deposits or accumulations to soften and slough or break off, getting blended into downstream process materials, representing significant contamination to the process. These large deposits are of particular concern because they represent contamination threats large enough to significantly affect product quality and process outcome even for processes traditionally considered very robust, such as some food, beverage and chemical production.
If gone undetected, product exposure can, in some cases, be harmful or even fatal. For this reason, regulators as well as the regulated industry have begun to look more closely at the source of the problem and search for ways to minimize it. An important part of this effort has been to implement more active preventative maintenance and inspection programs for valves. At some point, however, increasing human intervention becomes impractical and cost-prohibitive. Another part of the effort has been to reexamine the root cause of the problem. Specifically, the performance of current valve designs in sanitary process applications where valve maintenance efforts between production runs has been practically limited to in-situ cleaning, rinsing and steam sterilization.
As it turns out, process failures, although strongly skewed toward processes which have included valve designs which are dependent on sliding or rotating O-ring seals (i.e. ball valves, plug valves, tulip valves and kettle valves, have not been limited to these designs. Aoki, U.S. Pat. No. 3,949,963 and Lerman et. al., U.S. Pat. No. 4,822,570 disclose some typical examples of valve designs which may experience process failures. Even though many of the new sanitary processes being implemented include state-of-the-art weir diaphragm and radial diaphragm drain valve designs, failures still persist in these processes, albeit at a decreased rate. Typical examples of the above valve designs are Butler et. al., U.S. Pat. No. 5,277,401, Hoobyar, U.S. Pat. No. 5,152,500 and Ladisch, U.S. Pat. No. 4,836,236.
Diaphragm valves, with flexing diaphragms that allow valve actuation while isolating the process from moving valve parts and the surrounding outside environment, generally include less crevice areas and have smooth surfaces, all of which make them the best candidates available for use in CIP (clean-in-place) and SIP (steam sterilize-in-place) sanitary process applications. Of the other, more traditional valve designs, tulip and kettle valves are most frequently found in sanitary process applications. These valves are relatively inexpensive to install and maintain and are simple and mechanically reliable. Furthermore, even though they have more crevices as compared to diaphragm valves, it had been thought that their benefits were greater than their weaknesses and their weaknesses were not so serious as to restrict their use in processes requiring CIP and SIP steps before each batch, particularly in the more robust, food, beverage and chemical processing applications.
Inspection of valves commercially available today and of the background art reveal certain features common, not only to those drain valves making use of O-ring seals but also to both types of diaphragm drain valves. In particular, the seals formed between the valve body and the diaphragm or O-ring are made with the second, lower side of the bottom wall of the valve body internal cavity. As a result, the thickness of the bottom wall between the first (process) and second (non-process) sides form the wall of a well which is not possible to drain and serves to entrap and shelter process material, cleaning agents, rinse water and steam condensate. In some diaphragm designs, this well, though very large in diameter and, therefore, capable of harboring a large volume, relatively speaking, most areas can be washed clean except for the area immediately adjacent to the well wall. The problem associated with valves equipped with O-ring seals is, generally speaking, just the opposite. The wells above the seals tend to be very narrow because of the need for tight tolerances and a relatively close fit between the valve operating rod and O-ring/O-ring groove combination. Although the volume of the well tends to be much less, effective access for proper CIP and SIP procedure execution is not consistently possible.
Another problem area of valves associated with the design of bottom seal devices is their general tendency to have at least partially flat bottom walls to the valve internal cavity. While these walls may make these valves easier to fabricate, flat surfaces do not contribute to achieving positive drainage of materials from within the valve. Standing fluids, in many instances, can be as large of a threat of contamination as entrapped material, sometimes more because of the presence of large amounts of water, an important ingredient for microbial proliferation.
While the devices mentioned in this discussion may have certain weaknesses when used as drain valves or similar applications in sanitary processes, they may be perfectly adapted for other applications. It is the author's intent, however, to describe a valve design which includes several novel features which are flexible in concept and lend themselves to the improvement of more traditional drain valve designs. Among these are the elimination of the seal well in the bottom wall of the valve internal cavity which can be combined with the introduction of a bottom surface sloped toward the drain opening so that the bottom wall of the valve will actively urge process material, cleaning solutions, rinses and steam condensate to flow down and out of the valve. Other features include the option of rearranging secondary inlets and the drain outlet so as to encourage a swirling, scouring action of materials flowing through the valve so that more effective CIP and SIP results can be achieved. The new design will be illustrated in both diaphragm and O-ring type seal designs.